Slate v2 Op-family Twenty-third Slice

Supporting plan. For current queue and roadmap truth, see master-roadmap.md.

Goal

• Broaden mixed-inline non-empty Range deletion to spans that fully cover an interior inline subtree inside one supported top-level block.

Scope

• Keep deletion inside one supported top-level block.
• Support:
  • explicit non-empty Range
  • current non-empty selection when at is omitted
• Support fully covered interior descendants between the start and end edges.
• Avoid cross-block deletion and generic arbitrary tree ranges in this slice.

Phases

• Confirm the wider mixed-inline range-delete semantics and current helpers
• Write focused failing tests
• Implement the smallest honest core/API slice
• Sync package/public docs
• Verify the touched package/docs